Exposure compensation, explanation please?

I use Nikon D5100. I shoot 2 photos in shutter priority mode. First photo is at +1 EV 1/30 sec.f/5 ISO 1000. Second photo still at 1/30 sec.f/5 ISO 1000 and now +3 EV. But there's no difference when I compared it. They look the same, no change at all. Why? I'm confused. I'm new to DSLR.

If the two pictures you took have the same shutter speed, aperture, and ISO, then there shouldn't be a difference.
If you're adjusting it on shutter priority (TV) mode, then switching from +1 EV to +3 EV should slow the shutter way down, resulting in a brighter, though potentially less in focus photo.

The apertures should be different as in Shutter speed priority mode you set the shutter speed and it stays at that speed.

There should be a slight difference in exposure with the +3 EV brighter than the +1 EV shot.

Unless there's not enough light and the aperture was at maximum for the +1 EV so the lens could not open any further.

http://philip-northeast.suite101.com/how-to-use-exposure-compensation-a142730